PGBD5

PGBD5 is a domesticated piggyBac-family DNA transposase that retains active cut-and-paste transposition activity in human cells, catalyzing precise transposon excision and TTAA-preferential reintegration in a manner dependent on specific catalytic aspartic acid residues and on DNA substrates bearing piggyBac-like inverted terminal repeats (PMID:26406119). It localizes predominantly to the nucleus and is preferentially expressed in granule cell lineages of the brain and CNS (PMID:24180413), and it recognizes piggyBac-like elements through internal palindromic/inverted-repeat features rather than primary end sequence, mobilizing multiple natural piggyBac-like elements (PMID:33539889). In tumor cells, PGBD5 physically associates with genomic PGBD5-specific signal (PSS) sequences and drives site-specific structural DNA rearrangements at PSS breakpoints, and its ectopic expression is sufficient to transform primary human cells in vivo; both this oncogenic rearrangement activity and the transformation require intact transposase catalytic residues and functional NHEJ-mediated end joining (PMID:28504702). The genomic damage PGBD5 generates creates two therapeutically relevant dependencies: cells expressing catalytically active PGBD5 cannot tolerate loss of NHEJ and undergo apoptosis upon ATR inhibition, defining a synthetic-lethal interaction with ATR-dependent DNA-damage signaling (PMID:29093183). In vivo, Pgbd5 is required for tumor development in developmentally accurate SHH medulloblastoma mouse models, where its activity introduces somatic structural rearrangements—some bearing PGBD5 sequences at breakpoints—that recurrently disrupt tumor suppressors and oncogenes (PMID:38517960). Upstream, EZH2 represses PGBD5 such that EZH2 inhibition de-represses PGBD5, increases DNA damage, and sensitizes SMARCB1-deficient rhabdoid and epithelioid tumors to ATR (but not CHK1) inhibition (PMID:40794452).

1. 2013 Medium

   Before its enzymatic role was known, the basic localization and expression pattern of PGBD5 had to be established, showing it is a nuclear, neuronally enriched protein with unconventional chromatin association.

   Evidence Subcellular fractionation with DNase I and high-salt extraction of mouse brain nuclei plus in situ hybridization

   PMID:24180413

   Open questions at the time

   • Does not define a molecular activity or substrate
   • Unconventional (non-DNase/non-salt-releasable) nuclear retention left mechanistically unexplained
2. 2015 High

   Resolved whether the domesticated PGBD5 retained transposase function by demonstrating it catalyzes bona fide cut-and-paste transposition in human cells, establishing it as an active enzyme rather than an inert relic.

   Evidence In-cell transposition assays, active-site aspartate mutagenesis, and whole-genome integration-site sequencing

   PMID:26406119

   Open questions at the time

   • Did not identify endogenous genomic substrates acted on in vivo
   • No structural mechanism of catalysis or end recognition
3. 2017 High

   Connected the enzymatic activity to disease by showing PGBD5 binds endogenous PSS sequences, drives site-specific rearrangements, and transforms cells—dependent on catalysis and NHEJ.

   Evidence ChIP/physical association to PSS, catalytic mutants, in vivo transformation assays, assembly-based WGS of breakpoints

   PMID:28504702

   Open questions at the time

   • Mechanism by which breaks are channeled to NHEJ not resolved
   • How PSS recognition differs from transposon end recognition unclear
4. 2017 High

   Defined the therapeutic vulnerability created by PGBD5-induced damage, identifying NHEJ dependence and ATR synthetic lethality.

   Evidence NHEJ-deficient cells, nuclease-dead mutant controls, chemical screen of DNA-damage inhibitors, endogenous depletion, ATR inhibitor (AZD6738)

   PMID:29093183

   Open questions at the time

   • Did not establish the in vivo durability of ATR-inhibitor response
   • Did not address upstream regulation of PGBD5 expression
5. 2021 Medium

   Clarified substrate recognition rules by showing both human and mouse PGBD5 isoforms mobilize the closest natural piggyBac-like elements, likely via internal palindromic repeats.

   Evidence Transposition assays with two isoforms and two piggyBac-like elements, phylogenetics, integration-site analysis

   PMID:33539889

   Open questions at the time

   • Internal palindromic repeat dependence inferred, not proven by mutagenesis
   • Relationship between proper transposition and improper recombination unresolved
6. 2024 High

   Established causal in vivo oncogenic requirement for Pgbd5 in a developmentally faithful brain tumor model, linking its rearrangement activity to tumor initiation.

   Evidence Pgbd5-deficient mice, SHH medulloblastoma models, WGS of structural variants and breakpoint analysis

   PMID:38517960

   Open questions at the time

   • Why specific tumor suppressors/oncogenes are recurrently targeted is unexplained
   • Cell-of-origin determinants of PSS targeting not defined
7. 2024 Low

   Extended the tumor-promoting role to glioma via loss-of-function phenotypes, with a transcriptome-based link to PPAR signaling.

   Evidence siRNA knockdown, migration/invasion, apoptosis and cell-cycle flow cytometry, xenografts, transcriptome sequencing

   PMID:38577941

   Open questions at the time

   • PPAR pathway link is correlative transcriptomics without epistatic validation
   • No demonstration that glioma effects depend on transposase catalytic activity
8. 2025 Medium

   Identified an upstream regulator, showing EZH2 represses PGBD5 and that EZH2 inhibition de-represses it to potentiate ATR-inhibitor sensitivity.

   Evidence Tazemetostat treatment with PGBD5 measurement, ATR (elimusertib) vs CHK1 inhibitor comparison, DNA damage assays, patient-derived xenografts

   PMID:40794452

   Open questions at the time

   • Direct vs indirect EZH2 repression of the PGBD5 locus not resolved
   • DNA damage attributed 'at least in part' to PGBD5, leaving alternative contributors
9. 2025 Low

   Characterized cell-type-specific binding and mobilization of endogenous human piggyBac-like elements, extending substrate recognition to natural genomic copies.

   Evidence Chromosomal integration and chromatin-binding assays to endogenous pble copies across cell types (preprint)

   PMID:40766603

   Open questions at the time

   • Preprint without full biochemical reconstitution or mutagenesis validation
   • Determinants of cell-type-specific binding undefined

• The structural basis of PGBD5 end/PSS recognition and how its breaks are selectively engaged by NHEJ versus other repair pathways remain unresolved.
• No structural model of catalysis or substrate engagement
• Mechanism coupling transposase breaks to NHEJ and ATR signaling not defined
• Physiological (non-tumor) function in neurons unknown